This application is based upon and claims the benefit of priority of Japanese Patent Applications No. 2001-17264 filed on Jan. 25, 2001 and No. 2001-283612 filed on Sep. 18, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rotary pump with higher discharge pressure and a brake apparatus having the same.
2. Description of Related Art
A rotary pump, for example, an internal gear pump such as a trochoid pump or the like, is comprised of a drive shaft to be driven by a motor, an inner rotor and an outer rotor to be rotated by the drive shaft and a casing for containing the drive shaft and the inner and outer rotors. The inner and outer rotors contained in the casing form a plurality of teeth gap portions constituted by inner teeth portions of the outer rotor and outer teeth portions of the inner rotor which are in mesh with each other.
An intake port and a discharge port are separately disposed on opposite sides of a pump center line passing through the respective rotation axes of the inner and outer rotors. When the drive shaft is rotated for driving the pump, the inner rotor is rotated by the drive shaft on an axis of the drive shaft and, according to the rotation of the inner rotor, the outer rotor is rotated in the same direction since the inner teeth portions of the outer rotor are in mesh with the outer teeth portions of the inner rotor. As the respective volumes of the teeth gap portions between the inner and outer teeth portions are varied every turn of the rotating inner and outer rotors, fluid is sucked from the intake port and discharged to the discharge port.
In the conventional pump mentioned above, there is a drawback on producing higher discharge pressure that the fluid is likely to leak from a high pressure side to a low pressure side through a teeth top clearance between the outer and inner teeth portions at the teeth gap portion in which closed volume of brake fluid is maximum or the largest and through a teeth top clearance between the outer and inner teeth portions at the teeth gap portion in which closed volume of brake fluid is minimum or the smallest.
If each of the teeth top clearances mentioned above comes to near zero, the higher discharge pressure can be effectively produced. However, when a plenty of the pumps are manufactured through processes suitable for mass-production, it is practically difficult due to a manufacturing tolerance for all of the pumps to have dimensional accuracy to an extent that each of the teeth top clearances is always near zero. Accordingly, there inevitably exists a pump having the teeth top clearance larger than the near zero, which adversely affects on securing a target discharge pressure.
An object of the present invention is to provide a rotary pump with higher discharge pressure in which fluid leakage from the top teeth clearance between outer and inner gear portions is limited.
It is another object of the present invention to provide a brake apparatus having a hydraulic circuit in which the rotary pump mentioned above is disposed. The rotary pump is effective for increasing fluid pressure to wheel cylinders in the hydraulic circuit.
To achieve the object mentioned above, the rotary pump is composed of an outer rotor provided with inner teeth at an inner circumference thereof and an inner rotor provided with outer teeth at an outer circumference thereof so that the outer teeth is in mesh with the inner teeth so as to constitute a plurality of teeth gap portions therebetween, a drive shaft fitted to the inner rotor for rotating the inner rotor, and a casing provided with a rotor room in which the inner and outer rotors are rotatably contained with an outer circumference clearance between an inner circumferential surface of the rotor room and an outer circumferential surface of the outer rotor, and intake and discharge ports communicating respectively with the teeth gap portions that have a first closed region whose teeth gap volume is largest and a second closed region whose teeth gap volume is smallest.
With the rotary pump mentioned above, fluid is sucked from the intake port, compressed through the teeth gap portions and discharged from the discharge port when the drive shaft is driven, while fluid pressure difference between the intake and discharge ports is maintained by limiting brake fluid leakage though a teeth top clearance between the outer and inner teeth at the first and second closed regions. The outer rotor has deformation assist means for allowing the rotor to deform, when the fluid is discharged from the discharge port, so that the teeth top clearance of at least one of the first and second closed regions is more narrowed, resulting in increasing the volume efficiency and the discharge pressure of the rotary pump.
It is preferable that, as the discharge pressure is higher, the outer rotor more largely deforms.
A deforming amount of the outer rotor according to increase of the fluid discharge pressure and each amount of the teeth top clearance of the first and second closed regions at a zero fluid discharge pressure are set in advance so as to satisfy a condition, Q greater than QL, where Q is a theoretical fluid discharge amount per rotation and QL is a fluid leakage amount per rotation through both of the first and second closed regions.
If the amount of the teeth top clearance of the first or second closed region at a zero fluid discharge pressure is too large or the deforming amount of the outer rotor according to increase of the fluid discharge pressure (reducing amount of the teeth top clearance at the first or second closed region) is too small, QL=Q (zero fluid discharge amount) is established in a lower discharge pressure range since the fluid leakage amount becomes too large. In this case, high fluid discharge pressure can not be obtained since the volume efficiency xcex7 becomes 0% before reaching the turning point d, as shown by lines f or h in FIG. 4.
However, If Q greater than QL is satisfied as mentioned above, the volume efficiency xcex7once decreases as the fluid discharge pressure increases and, then, increases as the fluid discharge pressure increases, since the volume efficiency xcex7 has reached a turning point d before QL=Q is established, as shown by a solid line c in FIG. 4, resulting in realizing the higher fluid discharge pressure.
In the rotary pump, the outer circumference clearance constitutes high pressure and low pressure outer circumference chambers which communicate with the discharge and intake ports, respectively. The teeth gap portions communicating with the intake port has a first low pressure teeth gap portion adjacent to the first closed region, a second low pressure teeth gap portion adjacent to the second closed region and a third low pressure teeth gap portion provided between the first and second low pressure teeth gap portions. The fluid discharge pressure of the high pressure outer circumference chamber is applied to a first outer circumference surface of the outer rotor that is positioned radially outside the first low pressure teeth gap portion and a second outer circumference surface of the outer rotor that is positioned radially outside the second low pressure teeth gap portion at the outer circumference surface of the outer rotor. Therefore, the first and second outer circumference surfaces are pressed radially inward to deform the outer rotor due to pressure difference between the high pressure outer circumference chamber and the first or second low pressure teeth gap portion.
The fluid intake pressure of the low pressure outer circumference chamber is applied to a third outer circumference surface of the outer rotor that is positioned radially outside the third low pressure teeth gap portion. Therefore, the outer rotor is easily deformable radially outward at the third outer circumference surface and radially inward at the first and second outer circumference surfaces since there is no pressure difference between the low pressure circumference chamber and the third low pressure teeth gap portion and only first and second outer circumference surfaces are pressed inward.
The outer circumference clearance is provided with sealing members for preventing the fluid from flowing between the high and low pressure outer circumference chambers.
Preferably, the deformation assist means is each hollow teeth bottom of the outer rotor so that the teeth bottom of the outer rotor is positioned radially more outside than a locus of each teeth top of the inner rotor. Therefore, a thickness between the teeth bottom of the outer rotor and the outer circumference surface thereof is thinner.
The deformation assist means may be a chamfering portion at a corner corresponding to each teeth bottom among corners constituted by the inner circumference surface of the outer rotor and the opposite axial end surfaces thereof, a recess at an axial near middle point of each teeth bottom of the outer rotor, a ring shaped groove at an axial near middle point of the outer circumferential surface, a plurality of axial through-holes provided in the outer rotor, and a plurality of round holes on opposite axial end surfaces of the outer rotor.